Before having my daughter, I didn't think twice about going to the grocery store every day after work.

I'd pick up whatever my partner and I felt like having for dinner that night — some chicken and veggies to roast, a loaf of sourdough to slice up. Sometimes I'd even hit two stores in one afternoon, like Trader Joe's for a specialty item, then a local chain store for the basics at a lower price.

But toss a kid into that life and you'll drown pretty quickly. Both my partner and I work full-time: I'm a teacher by day, a freelance writer by whenever, and my partner works in television. Between our work and school drop-offs and pick-ups, the time sucked up by grocery shopping is a precious commodity. An added complication? We live in Los Angeles, where a five-mile drive can take 30 minutes in thick traffic.

By my estimation, one trip to a grocery store on any given day rarely takes up less than an hour of my time, and often far longer. Ultimately, we decided that we'd prefer to use that time in a different way — like cooking with our daughter, eating dinner as a family at home, reading books at bedtime, or doing some creative work of our own.

In fact, I recently did the math, and found that my family saves more than $750 a month, between the gas we save driving to the store, the impulse purchases we skip, and the hours' worth of extra productivity it frees up.

Here's a breakdown of how our spending and saving play out now that we've switched to online grocery shopping.

Our Amazon Prime membership costs us $119 a year. If you hate crowds and lines that come with post-work and weekend grocery shopping, the membership is worth it.

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The transition to grocery delivery wasn't terribly hard for us. We were already the family on the street with the most ridiculous number of Amazon boxes piled on the porch, and other than my occasional Target walkthrough (during which I almost solely buy wants, not needs), I haven't shopped regularly in retail stores for a while. Toilet paper, Ziploc bags, toothbrushes, cleaning supplies and the like have come right to our house for years. I buy most of my clothes online, too.

We pay $119 a year for our Amazon Prime membership — the two-day free delivery on Prime items makes that price feel worth it alone. The Prime membership also gives us an AmazonFresh membership, so we started and have stuck with this delivery provider.

If you agree with the adage 'time is money,' time spent shopping has a dollar value — we estimate that we make $640 dollars in time alone

I've come to agree with him to an extent. The one-liner feels especially relevant when you do any kind of freelance work, as I do. For example, if it takes me five hours to write an essay for a $400 fee, I know that one hour of my time is worth $80.

Let's stick with that value and apply it to everyday life. If one hour is worth $80 and one trip to the grocery store takes at least one hour, and the average family takes 1.6 trips per week (let's round up to two), that's $160 worth of time saved per week. And that's a whopping $640 per month.

To push this further, sometimes ordering groceries online helps me make money. Let's use Prime Now to explain. With Amazon's Prime Now service, you can have groceries delivered within two hours. And when you order at least $35 worth of goods, there is no delivery fee.

Again, the convenience and speed of this service are worth actual money. If I spend those same two hours writing (at about $80 an hour in value, remember), and I spend $50 on groceries, that's $160 minus $50. So while "grocery shopping," I actually made $110.

We save about $104 because we're not tempted to make impulse purchases

If I physically go into a Whole Foods, I will, without fail, purchase five or more items I had no intention of buying. Sometimes this works out and we discover a new cereal, granola bar, or kimchi we all like.

Other times, that $5.21 guacamole doesn't get eaten and it's money lost. I use guacamole as an actual example. I went to Whole Foods last month and that guacamole, a head of celery, and a bag of pretty terrible chickpea crackers were the casualties. Plus an hour of my time. In food alone, it was a loss of $13. Multiply that by the two trips per week, and I estimate we save $104 a month at the very least in impulse buys alone.

When we shop via AmazonFresh, the "Past Purchases" or "Buy It Again" options help us order our staples — it even shows how many times we've ordered them. It's difficult to "spot" an interesting new product while shopping online — not impossible, but screen-scrolling is far less thrilling than strolling down an aisle and tossing colorful packages into your non-virtual cart.

We save about $12 a month on the gas we don't use, too.

Don Ryan/AP Images

We save on gas as well, though it's a small amount per month. Our car goes an average of 17 miles per gallon in the city and gas cost $3.57 per gallon on average last month in LA. The closest Whole Foods to us is 3.5 miles away, so a seven-mile trip (there and back) uses 0.41 gallons, or $1.47. If, like the average family, we went to the market twice per week, we'd use about $11.75 per month on grocery store gas alone.

Here's what our monthly delivered grocery plan and bill actually look like for our family of three

Elaine Thompson/AP

We cook dinner at home on weekdays, and we tend to go out on weekends. We pack weekday lunches for two of us (my partner's work provides his lunch), and we make easy hot breakfasts on weekdays: eggs, toast, oatmeal, fresh fruit, cereal, et cetera.

We meal-plan very casually — on the drive home from our daughter's piano lesson, for example — and we order ingredients needed for those planned meals. Breakfast and lunch staples are on repeat and easy to add to our cart via our personal AmazonFresh browser.

Given that, here's what our orders looked like this past spring.

In March, we ordered groceries five times for a grand total of $301.08, plus $29 on (optional) tips. In April, we ordered groceries fives times for a total of $470.41, plus $38 in tips. And in May, we spent $407.92, plus $39 in tips. That averages out to $391.14 per month in groceries and about $35 monthly in tips.

As you can see, ordering groceries by delivery saves us money, especially on impulse buys and time. According to estimates made by the USDA, I'm on track with this idea. In June, the USDA estimated that "thrifty" families of two (with adults in my age bracket) spent $386.40 on food at home, "moderate" spenders bought $612.90 worth of groceries, and "liberal" spenders spent $766.60 on food for home. In the same categories, families of four would spend $646.80, $1,062 and $1,288.20, respectively.

While the USDA doesn't offer specific estimates on families of three, you can see that our average of $391.14 puts us closest to the spending of a "thrifty" family of two. If you add in our Prime membership dues (about $10 per month) and our tips ($35), we're at $436.14 per month, still below the "moderate budget" for the family of two.

We didn't start this journey in order to save money, but that's been a happy secondary result of the lifestyle change. First and foremost, we love that it frees up so much of our time to do other things.

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